A New Smoothened Antagonist Bearing the Purine Scaffold Shows Antitumour Activity In Vitro and In Vivo.

Ana María Zárate,Christian Espinosa-Bustos,Lucia Di Marcotullio,Andrew F G Quest,Angélica Fierro,Cristian O Salas,Simón Guerrero,Jaime Meléndez,Elena Loricchio,Miriam Caimano,Matías González-Quiroz,Andrea Calcaterra,Felipe Oyarzún-Ampuero,Adam Aguirre

doi:10.3390/ijms22168372

Abstract

The Smoothened (SMO) receptor is the most druggable target in the Hedgehog (HH) pathway for anticancer compounds. However, SMO antagonists such as vismodegib rapidly develop drug resistance. In this study, new SMO antagonists having the versatile purine ring as a scaffold were designed, synthesised, and biologically tested to provide an insight to their mechanism of action. Compound 4s was the most active and the best inhibitor of cell growth and selectively cytotoxic to cancer cells. 4s induced cell cycle arrest, apoptosis, a reduction in colony formation and downregulation of PTCH and GLI1 expression. BODIPY-cyclopamine displacement assays confirmed 4s is a SMO antagonist. In vivo, 4s strongly inhibited tumour relapse and metastasis of melanoma cells in mice. In vitro, 4s was more efficient than vismodegib to induce apoptosis in human cancer cells and that might be attributed to its dual ability to function as a SMO antagonist and apoptosis inducer.

Highlights

The Hedgehog (HH) signalling pathway plays a crucial role in early stages of embryo development
The structures and synthesis of the new 2,6,9-trisubstituted purines 4a–4s appear in Scheme 1
A nucleophilic substitution (SNAr) on C-2 was carried out using several amines or piperazine derivatives to obtain

Summary

Introduction

The Hedgehog (HH) signalling pathway plays a crucial role in early stages of embryo development. Aberrant activation of this pathway is linked to the occurrence of malignant transformation in different cancers that affect humans [4,5,6]. The active SMO triggers a downstream signalling cascade, which leads to the activation of GLI transcription factors (Gli, Gli and Gli3) that translocate into the nucleus and induce the expression of their target genes including GLI1 and PTCH1, among others which are pro-tumorigenic [7,8]. In several cancers including basal cell carcinoma (BCC) and medulloblastoma (MB), HH pathway is constitutively activated and related to ligand-independent mechanism, due to somatic mutations in PTCH1, SMO or SUFU genes [9]. Ligand-dependent activation has been shown in other malignancies, such as melanoma, pancreatic, lung, breast, renal, and colorectal cancers [2,6]

Methods

Results

Conclusion